Translation of Belgian language (7)
I believe the answer is:
bengali
'language' is the definition.
(thesaurus)
'translation of belgian' is the wordplay.
'translation of' is an anagram indicator (I've seen this in other clues).
'belgian' with letters rearranged gives 'BENGALI'.
(Other definitions for bengali that I've seen before include "Subcontinental" , "resident in Calcutta?" , "Asian language" , "may be Indian" , "tongue" .)